Hydraulic thermostat with double throw switch mechanism

ABSTRACT

A single point hydraulic thermostat having a housing enclosing a diaphragm assembly bearing upon a snap-acting spring mechanism with a point contact and controlling the position of a double throw switch mechanism. The housing is closed by a cover. The diaphragm assembly is supported from a bracket member that is connected to the cover by a slip joint. The bracket cooperates with a calibration screw for adjusting the position of the diaphragm. Hinge means are provided for both the bracket and the spring mechanism to prevent relative motion of the point contact between the diaphragm assembly and the spring mechanism during the calibration of the switch. The switch mechanism is fitted with an inclined set of fixed contacts at the top of the housing to facilitate the assembly into the housing of an insulating carrier member with movable contact members. An auxiliary spring member acts between the housing and the carrier to effect holding the top set of switch contacts closed during the initial movement of the spring mechanism until the snap-action occurs to reverse the switch setting so as to avoid contact chatter.

United States Patent Staples [541 HYDRAULIC THERMOSTAT WITH DOUBLE THROW SWITCH MECHANISM [52] US. Cl ..337/319, 219/393, 219/412,

337/311, 337/327 [51] Int. Cl. ..Hlh 37/20, l-lOlh 37/36, HOlh 37/60 [58] Field of Search ..337/309,3ll,318, 319, 323

[151 3,656,182 [451 Apr. 11,1972

Primary Examiner-Bemard A. Gilheany Assistant Examiner-Dewitt M. Morgan AttorneyRichard L. Caslin, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman 7] ABSTRACT A single point hydraulic thermostat having a housing enclosing a diaphragm assembly bearing upon a snap-acting spring mechanism with a point contact and controlling the position of a double throw switch mechanism. The housing is closed by a cover. The diaphragm assembly is supported from a bracket member that is connected to the cover by a slip joint. The bracket cooperates with a calibration screw for adjusting the position of the diaphragm. Hinge means are provided for both the bracket and the spring mechanism to prevent relative motion of the point contact between the diaphragm assembly and the spring mechanism during the calibration of the switch. The [56] References Clted switch mechanism is fitted with an inclined set of fixed con- UNTTED STATES PATENTS tacts at the top of the housing to facilitate the assembly into the housing of an insulating carrler member with movable 2,738,397 3/1956 Slonneger ..337/327 Contact members An auxiliary spring member acts between 3,344,252 9/ 1967 Hummel et a1. the housing and the carrier to effect holding the top set of 3,348,009 10/1967 Staples switch contacts closed during the initial movement of the 3,214,539 10/1965 Glaberso" et 31m spring mechanism until the snap-action occurs to reverse the 3,030,475 4/1962 Glaberson l 8 it h tti as t id t t h t 2,991,342 7/1961 Weber et al ..337/318 X 15 Claims, 8 Drawing Figures 33 HO 8| I 3 no 114 62 lo 12.0 2o 13 74 at,

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l I I I PAUL R. STAPLES V -94 BY2.Z fc: 94 n 2??) I ma ATTORNEY 1 HYDRAULIC THERMOSTAT WITH DOUBLE THROW SWITCH MECHANISM BACKGROUND OF THE INVENTION The present invention relates-to a hydraulic thermostat for use in a domestic oven as both a temperature limiting thermal switch means serving as a backup temperature control means for the oven thermostat control system during normal baking operations toprevent a runaway temperature condition in the event of a control failure, and also as an over-temperature, door interlock device in combination with a door latching mechanism to insure that the oven cavity may not be entered when the oven air temperature rises above about 580 F.

This invention is related to the art of self-cleaning ovens which utilize a pyrolytic method of cleaning the walls of the oven of food soil by raising the temperature of the walls into a heat-cleaning temperature range above about 750 F. for a sufficient length of time to transform the food soils into gaseous degradation products which are then oxidized and finally discharged from the oven cavity. The details of this method and of a preferred embodiment of an oven design in which it may be carried out are fully disclosed in the US. Pat. of Bohdan Hurko No. 3,121,158, which is assigned to the General Electric Company, the assignee of the present invention.

Once the method of pyrolysis was perfected and adopted for the automatic heat-cleaning of baking ovens, many different systems of applying the heat, governing the method of heat transfer and controlling the cleaning cycle were devised to obtain the desired results. To obtain the maximum reliability, standard components are used where possible to take advantage of the years of engineering development and knowhow gained by working with the components, and they were arranged in fail-safe combinations so that after years of trouble-free usage of the oven a failure of a component would not constitute a safety hazard. Instead, the failure of one of these components would render inoperative the heating circuit, function or system in which the component operates.

The present invention is concerned with the dual function of insuring that during a cooking operation the oven air temperature does not rise above about 580 F. in the event of a failure of one of the temperature control elements, and secondly to insure that the housewife may not unlatch the oven door during a heat-cleaning operation unless the oven air temperature returns below about 580 F. This invention is an improvement over an earlier invention of Samuel C. Jordan and Teamus Bowling in U.S. Pat. No. 3,484,858, entitled Self-Cleaning Oven With Over-Temperature Protective System.

The principle object of the present invention is to provide a hydraulic thermostat with improved accuracy by simplifying the mounting means for the diaphragm assembly and its method of calibration as well as to prevent relative movement at the contact point between the diaphragm and the snap-acting spring mechanism during the operation of the thermostat.

A further object of the present invention is to provide a hydraulic thennostat of the class described with a novel double throw switch mechanism with switch contact placement to facilitate the ease of assembly of the switch.

A further object of the present invention is to provide a hydraulic thermostat of the class described where the switch mechanism incorporates an auxiliary spring that serves to hold one set of contacts closed during the initial movement of the spring mechanism before the snap-action occurs so as to prevent contact chatter.

SUMMARY OF THE INVENTION The present invention, in accordance with one form thereof, relates to a hydraulic thermostat that incorporates a housing supporting a diaphragm assembly that bears against a snap-acting spring mechanism that controls the position of a double throw switch mechanism. The diaphragm assembly is supported on a resilient cantilever arm of a bracket member, and the assembly is in point contact with the spring mechanism. The spring mechanism has a hinge axis substantially coinciding with the hinge axis of the cantilever arm so there is substantially no relative motion at the said point contact during the calibration of the switch mechanism.

Another feature of the invention is that the electrical switch has an insulating carrier member joined at one end to the spring mechanism and supported in the housing for generally straight-line motion. This carrier has a crosshead at its other end with a movable switch contact member supported on each end thereof. Fixed contact means are mounted in the housing for engagement by one of the movable contact members respectively. Each fixed contact means is mounted in opposition to the other fixed contact means to establish a double throw switch mechanism. An auxiliary spring is positioned between the housing and the carrier member to effect holding of one of the set of contacts closed during the initial movement of the spring mechanism and until the snap-action occurs to reverse the switch setting so as to avoid contact chatter.

BRIEF DESCRIPTION OF THE DRAWINGS My invention will be better understood from the following description taken in conjunction with the accompanying drawings and its scope will be pointed out in the appended claims.

FIG. 1 is a longitudinal, cross-sectional, elevational view on an enlarged scale taken generally through the center of the housing of a hydraulic thermostat embodying the present invention.

FIG. 2 is a top plan view of the thermostat of FIG. 1 with some parts broken away and others in cross-section to show the nature of the slip joint for connecting the bracket supporting the diaphragm assembly to the cover of the housing, as well as showing the nature of the double throw switch mechanism.

FIG. 3 is a transverse, cross-sectional, elevational view taken on the line 3-3 of FIG. 1 and showing the nature of the switch mechanism when the lower set of switch contacts are closed in the heating circuit used during a cooking operation.

FIG. 4 is a cross-sectional, elevational view similar to that of FIG. 1 but after the diaphragm has expanded to cause the snap-action of the spring mechanism and the actuation of the switch mechanism to its opposite position.

FIG. 5 is a transverse, cross-sectional, elevational view, taken on the line 5-5 of FIG. 4, showing the switch in its opposite or reversed position where the upper set of switch contacts are closed.

FIG. 6 is a schematic diagram of the power and control circuits for a self-cleaning electric oven embodying the thermostat or temperature switch of the present invention.

FIG. 7 is a plan view on a reduced scale of the combined blade and amplitude spring of the snap-action spring mechanism for the present thermostat.

FIG. 8 is a fragmentary, perspective, exploded view of the slip joint between the cover plate and one end of the bracket member which supports the diaphragm assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to a consideration of the drawings, and in particular to FIG. 1, 10 represents a hollow housing of the thermostat 9 of the present invention that is formed by a box-like base 11 of molded insulating material such as a phenolic resin or-the like with a pair of metal cover plates 13 and 14 for substantially closing the base and completing the housing. The shape of the box-like base 11 is generally rectangular in plan view as is seen in FIG. 2, and it has a bottom wall 15 that is closed at the left side of the base but open at the right side as is clear from FIG. 1. Then there are opposite end walls 17 and 18, and opposite side walls 20 and 21. The complete top wall is open, and it is adapted to be closed by the two cover plates 13 and 14. The cover plate 13 is held in place by a series of four screws 23 arranged at the four corners of the cover and threaded into suitable openings in the base. Rising up from the left side of the cover 13 is a flange 19 which serves as a mounting strap for the thermostat, as is best seen in FIG. 8. The second cover member 14 is of folded sheet metal configuration of U-shape, as is best seen in the side elevational view of FIG. 1. The cover 14 has a top portion 25, a vertical portion 26 which overlies the end wall 18 and a bottom portion 27 which covers the opening in the right side of the bottom wall 15 of the base. No screws are needed to fasten the second cover 14 to the base since its U-shape provides a spring action which grips the base tightly.

This thermostat comprises three principal elements in addition to the housing namely, an expansible member or diaphragm assembly 30, a snap-acting spring mechanism 32 and a single pole, double throw switch mechanism 34. The general nature of this thermostat is present in a family of thermostats of the present inventor, as for example in my US. Pat. No. 3,293,394, entitled Temperature Responsive Control Device With Snap Acting Switch, which is assigned to the General Electric Company, the assignee of the present invention. Another modification is shown in my pending patent application Ser. No. 737,139, now U.S. Pat. No. 3,514,733, entitled Snap-Action l-Iot Wire Power Switching Relay which was filed on June 14, 1968, and is likewise assigned to the same assignee.

The base 11 is divided into two substantially equal sections by a transverse partition 36 forming at the left an expansion chamber 37 that houses the diaphragm assembly 30 and at the right a switch compartment 38 in which the switch mechanism 34 is housed. The transverse partition 36 is left open at the bottom as at 36', and there is a horizontal partition 40 which extends from the bottom edge of the transverse partition 36 to the end wall 18 as is best seen in FIG. 1. This opening 36' accommodates the elongated snap-acting spring mechanism 32 which underlies the diaphragm assembly 30 at one end as well as the spring mechanism 34 at the other end.

The snap-acting spring mechanism 32 is the same as is shown in my earlier US. Pat. No. 3,293,394. This spring mechanism is in the form of a combined blade and amplitude spring that is generally of elongated rectangular configuration as is best seen in plan view in FIG. 7. It is made of thin sheet, spring stock such as beryllium copper or the like. This blade is provided with a pair of spaced, longitudinal slots 42, 42, which stop short of the ends of the blade so as to define three longitudinal strips; namely, a center strip 43 and two side strips 44, 44 that are each joined to the other at each end. Looking at FIG. 1, the blade 32 is formed upwardly to retain a natural upward bowed condition. The left end 46 may be called the supported end of the blade, while the right end 47 may be considered as the free or bistable end of the blade. The blade should be restrained from moving in a horizontal plane and this is accomplished by interlocking the supported end 46 of the blade with the base 11. Looking at the plan view of the blade in FIG. 7, the blade end 46 has a pair of oppositely directed ears 49 which are each adapted to fit snugly into a vertical slot 51 formed in the base 11 as seen in both FIGS. 1 and 2. Thus, the cars 49, 49 of the blade 32 are lowered into the vertical slots 51, 51 after the free end 47 of the blade is first inserted through the opening 36 in the base 11 into the third compartment 41 beneath the switch compartment 38. For calibration purposes, a vertical adjusting screw 53 is threaded up through the bottom wall of the base 11 and is adapted to be in contact with the underside of the supported end 46 of the blade 32 at a point on an imaginary central line connecting the supporting ears 49, 49 as is best seen in FIGS. 1 and 2.

At this stage in the description of the combined blade and amplitude spring 32 it is unstable in that it is supported at only one point; namely, on the calibration screw 53. In addition, the two side strips 44, 44 of the blade have portions folded downwardly to form a V-section knife-edge 55 for bearing upon a support pad 56 formed on the bottom wall of the base 11. Each knife-edge 55 is opposite the other so that the two knife-edges are located in an imaginary transverse line with each other. Thus, the blade 32 is provided with a three-point support system; namely, the calibration screw 53 at the supported end 46 of the blade and the two knife-edges 55, 55 at the two side strips 44, 44 of the blade.

The diaphragm assembly 30 is adapted to bear against the center strip 43 of the blade. In order to obtain accurate results, there is a point contact between a wear plate 58 fastened on the bottom of the diaphragm and a raised, semispherical embossment 60 formed in the center strip 43. Notice that this point contact is located within the area bounded by the three-point support system of the calibration screw 53 and the two knife-edges 55,55.

Having described above the thermostat housing 10 and the snap-acting spring mechanism 32, attention will now be given to the expansible member or diaphragm assembly 30 within the expansion chamber 37. It is in reality a hydraulic-filled bellows or diaphragm assembly that converts volumetric expansion or contraction into rectilinear motion acting upon the spring mechanism 32. A suitable high temperature fluid for filling the system would be a eutectic mixture of sodium and potassium (NaK). Into the side of the diaphragm assembly is connected a capillary tube 62 of about one foot in length. This tube is adapted to extend out of the base 11 so that its free end may be positioned within the area wherein the temperature is to be controlled, such as a baking oven. Provided on the free end of the tube would be an elongated temperature bulb or probe (not shown), as is conventional in this art. The bulb, capillary tube and diaphragm is preferably made of stainless steel. As is best seen in FIGS. 1 and 2, the transverse partition 36 is provided with a groove 64 in the top surface thereof for receiving the capillary tube 62. The capillary tube is held in this groove by the cover 13 that closely overlies the same.

One of the important features of this invention, is the method of mounting the diaphragm assembly 30 in the thermostat housing 10. The diaphragm assembly 30 is supported on an adjustable bracket member 66 which is associated with the cover 13. The bracket member 66 is a small sheet metal part that is connected adjacent one end 68 to the cover 13 by a slip joint which is easy to assemble without the need of separate fastening means. See FIG. 8. The edge of the cover 13 formed with the flange or mounting strap 19 is provided with a bayonet slot 101 of generally T-shaped formation having an elongated entrance slot 103 arranged in the edge 100 and a clearance slot 105 in the cover to overlie a portion of the expansion chamber 37. The end 68 of the bracket member 66 is folded first on a line 107 and then in an opposite direction on a line 108 to form a vertical, upward tip 110, a horizontal portion 112 and a vertical, downward leg 70. Notches 114, 114 are cut in the opposite sides of the horizontal portions 112 and the folded edge 108. To assemble the slip joint, the upward tip of the bracket 66 is inserted upwardly through the entrance slot 103 in an inclined direction so that the comers 116 in the horizontal portion 112, that are formed after the notches 114, 114 are cut, may slip through the entrance slot 103 thereby allowing the notches 114, 114 to slip into the clearance slot 105. Then when the bracket 66 is straightened by a counterclockwise movement, the corners 116 rest on the seats 118, 118 of the bayonet slot 101 at the margins between the entrance slot 103 and the clearance slot 105. Moreover, the lower edges 120, 120 of the slots 114, 114 are raised up to bear against the underside of the cover 13 as is best seen in FIG. 1, and the upward tip 110 presses against the mounting strap 19. The vertical leg 70 is braced against the end wall 17 of the base 11 by means of the engagement of a semi-spherical raised embossment 71, as is seen in FIG. 1. This pressure on the bracket member 66 that is exerted by the base wall 17 serves as the locking force for the slip joint.

Rising up from the bottom edge of the rigid leg 70 of the bracket member 66 is a resilient cantilever arm 73 which has a hinge point or axis 74 at the said bottom edge and it has a free end 75 that stops just short of the underside of the cover 13. Near the mid-portion of the arm 73, the diaphragm assembly 30 is connected on the underside thereof. The diaphragm assembly has on its top wall a vertical pin 77 which extends through a suitable opening in the arm 73. A speed nut 79 is then forced over the pin 77 and and against the top surface of the arm 73 for holding the diaphragm assembly rigidly in place on the arm.

. As mentioned previously, the bottom portion of the diaphragm assembly 30 has a wear pad 58 seated upon the raised embossment 60 of the snap-acting spring mechanism 32 to provide a single point contact. The thermostat must be preset or calibrated so that it will operate at a single temperature nominally 580 F., but for my purposes it can be a single temperature anywhere between about 560 F. and 600 F. Thus, a second calibration screw 81 is threaded down through the cover 13, and it is adapted to bear against the free end 75 of the cantilever arm 73 as is best seen in FIG. 1. During the calibration procedure, the upper calibration screw 81 is turned in both clockwise and counter-clockwise directions with the objective being to effect the alternate opening and closing of the switch mechanism 34 when the upper screw 81 has an angular sweep of about 70. This 70 sweep can be obtained by adjusting the lower calibration screw 53 until it is obtained. This provides good contact forces and snap action. Then set the upper calibration screw 81 until the normally closed contacts 93 and 93' open and contacts 92 and 92' close at the design temperature of 580 F.

You will note that the raised embossment 60 of the spring blade 32 moves during its vertical movement about a radius that is generated from the hinge axis of the blade or the imaginary line 125 drawn between the opposing ears 49 of the blade at the supported end 46 of the blade as is seen in FIG. 2. Similarly, the wear pad 58 being supported from the cantilever arm 73 moves about a radius that is generated from the hinge axis 74 of the arm; namely, at the bottom edge of the rigid leg 70 of the bracket member 66, and that this hinge axis 74 substantially coincides with the hinge axis 125 of the blade 32 such that there is substantially no relative movement between the wear pad 58 and the raised embossment 60 during the adjustment of the second calibration screw 81. This is important because the coefficient of static friction is greater than the coefficient of sliding friction, therefore, there would be an erratic and unpredictable relative movement if relative movement were allowed between these two parts 58 and 60 which would make difficult the proper calibration of the switch mechanism.

Now turning to a consideration of the double throw switch mechanism 34, the free end 47 of the spring blade 32 is connected to the lower portion 83 of an insulating carrier member 84 before the cars 49, 49 of the blade are lowered into the vertical slots 51, 51 of the base 11. Looking at the transverse cross-sectional elevational view of FIG. 3, the carrier member is shown as having a generally T-shaped configuration with a vertical shank 86 and a horizontal cross-head 88 at the top. The switch compartment 38 is provided with a longitudinal central partition 90 which is slotted transversely as at 89 to accommodate the carrier member 84 therethrough. Thus, the partition 90 serves as guide means for the carrier member 84,

as well as an insulating means between the various switch components. Notice that this longitudinal partition 90 is not visible in FIG. 1 because this cross-sectional view was cut just to the other side of the partition 90. The crosshead 88 of the carrier member 84 carries a bridging contact 92 at one end and a bridging contact 93 at the other end. Two pairs of fixed contacts 92' and 93 are arranged in the housing. Each fixed contact 92 and 93 is furnished with a terminal blade 94 which is fastened in the base 11 and extends to the outside of the housing for ease in making an electrical connection thereto. The fixed contacts 92' are adapted to be engaged by the bridging contact 92, and similarly the two fixed contacts 93 are adapted to be engaged by the bridging contact 93. One pair of fixed contacts 92 is mounted to be in opposition to the other pair 93' such that movement of the carrier 84 in one direction closes a circuit through one pair of fixed contacts and opens a separate circuit through the other pair of fixed contacts in the manner of a double throw switch. The fixed contacts 93 are arranged beneath the crosshead 88 on the horizontal partition 40, while the opposite pair of fixed contacts 92' are arranged at an inward and upward angle from the side wall 20 of the base 11 as is best seen in F IG. 3. This angular placement of the upper set of fixed contacts 92' facilitate the ease of assembly of the carrier member 84 into the base 11 through the slot 89.

The carrier member 84 is capable of a slight straight line, up and down motion. However an auxiliary spring 95 of generally U-shaped or hairpin configuration is mounted between the housing 10 and the carrier member 84 at an inclined angle of about 30 from the longitudinal partition 90, as is best seen in FIG. 3. The biasing action provided by this auxiliary spring 95 serves to exert a force tending to close the bridging or movable contact 92 with the fixed contacts 92'. The function of this spring is to maintain contact pressure between the bridging and fixed contacts 92 and 92' respectively during the creep portion or initial portion of the movement of the spring blade 32 during the contact breaking of this top set of contacts so as to prevent contact chatter or teasing of the contacts which might otherwise result in the welding of the contacts over a period of use. The circuit through this top set of contacts 92 and 92 is a low current low voltage circuit of about 5 amperes 1 15 volts and it is closed during the high temperature cleaning cycle of the oven. The circuit through the lower set of contacts 93 and 93' is a high current high voltage circuit of about 21 amps 250 volts and it is the power circuit used during the cooking operations of the oven as well as the circuit for the electric solenoid latch release in the normal cleaning operation and thus prevents solenoid energization above 580 F.

The single point thermostat 9 of the present invention is designed to be used as a control component of a self-cleaning electric oven whose power and control circuits are illustrated in the schematic diagram of FIG. 6. The oven is furnished with an electrical service of three-wire Edison source of power; nominally of 240 volts, single phase, 60 cycle, A.C. which is usually available in the average residence having adequate wiring. This voltage source is fed to the oven through a threewire cable having a pair of line wires L1 and L2 with a voltage of 240 volts therebetween, and a grounded neutral conductor N with half voltage or volts measured across any line wire L1 or L2 with the neutral conductor N for supplying the electrical load of the oven. This electrical load is characterized by three heating elements; a baking element 130, a broiling element 132 and a mullion heater 134. The bake element is usually located adjacent the bottom wall of the oven, the broil element 132 is usually located adjacent the top wall of the oven and the mullion heater 134 is usually wrapped around the outside of the oven liner adjacent the front opening for replenishing the heat lost through and around the door opening during a high temperature, heat-cleaning or pyrolytic cycle. These heating elements 130, 132 and 134 are arranged in circuits in combination with an oven selector switch 136 for setting up different combinations of heating elements at different voltages to obtain a variety of heating rates. A manually settable oven thermostat 138 is also available for controlling the temperature within the oven at preselected temperatures during baking operations and a maximum temperature during oven cleaning operations. Such an oven thermostat 138 controls a hot wire relay 140 that is in series with the heating elements 130, 132 and 134 for opening and closing the power circuit to the heating elements as a function of oven temperature with relation to the temperature predetermined or preset by the thermostat 138. The single point thermostat 9 of the present invention is not the oven thermostat 138 of the circuit diagram. The present invention of a single point thermostat 9 has a double throw switch 34 that is identified in the circuit diagram of FIG. 6. Remember this double throw switch 34 includes one set of contacts 92, 92 and another set 93, 93'.

The oven selector switch 136 is provided with a series of line terminals L N, L1 and L2, as well as a series of three load terminals K, J and P. This oven switch 136 is provided with a plurality of switch contacts 142-150. These switch contacts are labeled with the particular cooking or cleaning operation that is involved when such contacts are closed. For example, during a Baking or a Time-Baking operation contacts 142, 143, 148 and 149 are closed. During a Broiling operation, contacts 146 and 147 are closed. During a Cleaning cycle contacts 143, 144, 145, 146, 149 and 150 are closed.

The Baking" circuit has the bake element 130 operating at full wattage across lines L1 and L2 at 240 volts through the temperature switch 34 and its switch contacts 93 and 93' to the line terminal L1 through switch contacts 142, 143 to load terminal K and through the bake element 130 to the hot wire relay 140 and through a smoke eliminator 155 to line L2. During the baking cycle the other two heating elements 132 and 134 are also energized. They are in a series circuit connected back to the temperature switch 93, 93' by means of lead 157 to line terminal L1 through oven switch contacts 148, 149 to load terminal P, and then through the mullion heater 134 and the broil element 132 through the hot wire relay 140 and back to line L2.

In the Broiling circuit only the broil element 132 is energized and it is across lines L1 and L2 through the temperature switch contacts 93 and 93 and lead 157 to line terminal L1 through switch contacts 147, 146 to load terminal J and then through the broil element 132 and the hot wire relay to the line L2.

If there is a component failure during a cooking operation of either baking, time-baking or broiling and the oven temperature were to rise above the pre-set temperature of the oven thermostat 138 and reach an oven temperature of say 580 F. then the temperature switch 34 would be operated by the single point thermostat 9 of the present invention to open the circuits through switch contacts 93, 93 thereby de-energizing the heating elements and preventing a runaway temperature condition. Thus, this temperature switch 34 of the single point thermostat 9 serves as an overtemperature limit control when the oven is in any normal cooking operation. Thus, in the event of a malfunction of the primary temperature control, any hazard due to overheating of the oven during the baking, broiling and time-baking mode of operation is eliminated.

The second set of switch contacts 92, 92 of the temperature switch 34 is arranged to be in an operating circuit only during the heat-cleaning mode of operation. During the cleaning operation the three heating elements 130, 132 and 134'are connected in parallel at half voltage across line L2 and neutral conductor N in order to obtain a heating rate somewhat lower than the heating rate during the baking operation. At temperatures below about 580 F. the switch contacts 93 and 93' of the temperature switch 34 are closed in the solenoid circuit to allow solenoid actuation. At temperatures above 580 F. contacts 93 and 93 are open thus preventing the electrical circuit for the door latch solenoid from being actuated. At temperatures above that critical temperature, the opposite set of contacts 92 and 92 are closed to provide power for the cooling fan 172. For a more thorough discussion of the oven door latching environment in which the present invention is used reference is made to the aforementioned Jordan and Bowling US. Pat. No. 3,484,858.

In order to set up the heat-cleaning circuit there are several preliminary operations that must be perfonned first; As mentioned previously, it is imperative that the oven door first be closed and then locked before the heat-cleaning cycle is initiated, and also that the door remain closed and incapable of being opened while the oven temperatures are above normal cooking temperatures. The door latch mechanism is shown schematically only as a reciprocating bar 160 that is actuated by the door latch and is provided with an automatic latching means 162 in the form of a spring biased, pivoted hook member which locks the door latching mechanism 160 in both its open and its closed positions. Thus, this latching means 162 must be disengaged before the oven door lock lever 160 may be shifted. This is accomplished by connecting a solenoid 164 across line L1 and neutral conductor N and in the following circuit through switch contacts 93, 93' to lead 157 to a momentary latch release switch 156, and then through the solenoid 164 to switch contacts 166, 167 of the oven switch 136 and then through leads 169 and 170 back to neutral conductor N. Thus, at temperatures below the operating temperature of the temperature switch 34, that is below 580 F it is possible to shift the oven door latch by closing the momentary latch release switch 156 thereby energizing the solenoid which picks up the automatic locking device 162 and releases the door latch mechanism 160. However at temperatures above normal cooking temperatures, that is above 580 F temperature switch 34 will be actuated thereby opening the circuit through switch contacts 93 and 93 which disables the solenoid circuit and prevents access to the oven during the heatcleaning cycle. The closing of the second set of switch contacts 92 and 92' energizes a cooling fan motor 172 and other auxiliary components which are used during the high-temperature heat-cleaning cycle. It is not felt necessary to go into any further detail of the power and control circuit since the present invention is centered around the single point thermostat 9' and its temperature switch 34 rather than in the overall circuit and oven combination in which it has been used.

Modifications of this invention will occur to those skilled in this art, therefore it is to be understood that this invention is not limited to the particular embodiments disclosed but that it is intended to cover all modifications which are within the true spirit and scope of this invention as claimed.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A fixed point, double throw thermal switch comprising an insulating housing with a removable cover, said housing having a separate expansion chamber enclosing both a diaphragm assembly and a snap-acting spring mechanism that is acted upon thereby, said housing also having a pair of electrically isolated switch compartments supporting a double throw switch mechanism, there being an insulating carrier member joining the said spring mechanism to the said switch mechanism, one switch compartment enclosing one set of normally closed switch contacts of the switch mechanism for low temperature operation and the other switch compartment enclosing an alternate set of normally open switch contacts of the switch mechanism for high temperature operation, there being a critical operating temperature for the switch that falls between about 500 F. and about 750 F., whereby at temperatures below the critical temperature, the double throw switch mechanism is in its normal cooking position and at temperatures above the critical temperature, the switch mechanism is in its normal oven cleaning position so that the thermal switch serves as an over-temperature protective means during normal cooking operations and as a lock-out means during a high temperature oven cleaning cycle, said diaphragm assembly being supported on an adjustable bracket member carried by the said housing cover.

2. A fixed point, thermal switch as recited in claim 1 wherein the adjustable bracket member supporting the said diaphragm assembly is connected adjacent one of its ends to the removable cover, and an adjustable calibration screw extends through the said cover member and engages the opposite end of the bracket for determining the relative position of the diaphragm assembly with respect to the spring mechanism.

3. A fixed point, thermal switch as recited in claim 1 wherein the adjustable bracket member is connected adjacent one of its ends to the removable cover by a slip joint, said bracket having a rigid leg extending down from the slip joint, said leg being-braced against one wall of the housing to lock the slip joint in place, said bracket having a resilient cantilever arm rising up and out at an angle from the bottom of the rigid leg, the said diaphragm assembly being mounted on the cantilever arm and having a wear pad seated on a pressure point of the spring mechanism, and a calibration screw means extending through the said cover member and engaging the free end of the cantilever arm for determining the relative position of the diaphragm assembly with respect to the spring mechanism.

4. A fixed point, thermal switch as recited in claim 3 wherein the adjustable cantilever arm supporting the diaphragm assembly has a hinge axis that substantially coincides with the said hinge axis of the snap-acting spring mechanism such that there is substantially no relative motion between the wear pad of the diaphragm assembly and the pressure point of the spring mechanism during the calibration of the thermal switch.

5. A fixed point, thermal switch as recited in claim 1 wherein the said double throw electric switch means includes an insulating carrier member joined adjacent one end to the said spring mechanism and being supported for generally straight-line motion, said carrier member having a crosshead with a bridging contact member supported on each end, and two pairs of fixed contacts mounted in the housing, each pair of contacts being adapted to be engaged by one of the bridging contacts, one pair of fixed contacts being mounted in opposition to the other pair such that movement of the carrier in one direction closes the circuit through one pair of fixed contacts and vice versa, and auxiliary spring means acting between the housing and the carrier member to bias the carrier in an angular direction with respect to the direction of movement of the carrier so as to give the carrier a slight rocking action to maintain contact pressure with at least one set of bridging and fixed contacts during the initial creep portion of the spring mechanism before it snaps into its opposite position so as to prevent contact chatter.

6. A fixed point, thermal switch as recited in claim 5 wherein one pair of fixed contacts is arranged at an acute angle with respect to the direction of movement of the carrier and substantially overhangs the crosshead, and the other pair of fixed contacts is arranged at a transverse angle to the direction of movement of the carrier and underlies the crosshead, the said auxiliary spring means acting in an upward biasing direction to maintain the overhanging set of contacts closed until the spring mechanism snaps into its reversed position.

7. A hydraulic thermostat comprising a housing enclosing a diaphragm assembly, a snap-acting spring mechanism and an electrical switch means, the diaphragm assembly bearing against the spring mechanism, and the spring mechanism being joined to the switch means for making and breaking an electrical circuit as a function of the expansion and contraction of the diaphragm assembly according to the direction and the extent of the temperature change of a remote body, said housing having a removable cover, said diaphragm assembly being supported from the cover by a bracket member, said bracket having a leg extending down from the cover and a resilient cantilever arm rising up at an acute angle from the bottom of the leg, the diaphragm assembly being mounted to the bottom of the cantilever arm, and a calibration screw means extending through the cover and engaging the free end of the resilient arm for varying the relative position of the diaphragm assembly with respect to the spring mechanism.

8. A hydraulic thermostat as recited in claim 7 wherein the diaphragm assembly is in point contact with the spring mechanism, the spring mechanism having a hinge axis substantially coinciding with the hinge axis of the cantilever arm so there is substantially no relative motion at the point of contact during the calibration of the said switch means.

9. A hydraulic thermostat as recited in claim 7 wherein the said bracket member is joined to the cover by a modified bay onet slot connection, said leg of the bracket being braced against one wall of the housing to lock the bracket to the cover.

10. A hydraulic thermostat as recited in claim 9 wherein the said electrical switch means comprises an insulating carrier member having a crosshead supporting bridging contact means adjacent each end thereof, fixed contact means mounted in the housing for cooperation with the adjacent bridging contact means, and an auxiliary spring means arranged between the housing and the carrier member to bias the carrier into a slight rocking action as it moves upon movement of the diaphragm assembly to maintain contact pressure during the creep portion of the spring mechanism before the spring mechanism snaps so as to avoid contact chatter.

l 1. A hydraulic thermostat as recited in claim 9 wherein the said electrical switch means comprises an insulating carrier member having a crosshead supporting a bridging contact means adjacent each end thereof, fixed contact means mounted in the housing for cooperation with the adjacent bridging contact means, one fixed contact means being located beneath the adjacent bridging contact means, the other fixed contact means being disposed at an inclined angle above the other bridging contact means, and an auxiliary spring means acting between the housing and the crosshead to maintain contact pressure between the movable contact and the inclined fixed contact means during the creep portion of the spring mechanism before it snaps and opens this set of contacts and closes the opposite set of contacts.

12. A hydraulic thermostat comprising a housing enclosing a diaphragm assembly bearing upon a snap-acting spring mechanism that controls an electrical switch, a cover for closing the housing, the diaphragm assembly being supported on a resilient cantilever arm of a bracket member, calibration means bearing upon the cantilever arm for adjusting the position of the diaphragm, the diaphragm assembly being in point contact with the spring mechanism, the spring mechanism having a hinge axis substantially coinciding with the hinge axis of the cantilever arm so there is substantially no relative motion at the point contact during the calibration of the said switch, the said electrical switch including an insulating carrier member joined at one end to the spring mechanism and supported in the housing for generally straight-line motion, said carrier member having a crosshead at its other end with a movable switch contact member supported on each end, a fixed contact means mounted in the housing for engagement by one of the movable contact members respectively, each fixed contact member being mounted in opposition to the other fixed contact member to establish a double throw switch mechanism, an auxiliary spring means acting between the housing and the carrier member to effect holding of one of the set of contacts closed during initial movement of the spring mechanism and until the snap action takes place to reverse the switch setting so as to avoid contact chatter.

13. A hydraulic thermostat as recited in claim 12 wherein the top fixed contact is positioned in an inward and upward inclined angle overlying the crosshead to facilitate the assembly of the carrier member into the housing, while the lower fixed contact means underlies the crosshead, the said auxiliary spring biasing the carrier in a direction generally toward the top fixed contact means.

14. A hydraulic thermostat as recited in claim 12 wherein the bracket member is connected to the housing cover by a slip joint, the bracket having a rigid leg extending down from the slip joint and braced against one wall of the housing to lock the slip joint in place, the resilient cantilever arm of the bracket being hinged to the bottom portion of the rigid leg.

15. A hydraulic thermostat comprising a housing enclosing a diaphragm assembly bearing upon a snap-acting spring mechanism that controls an electrical switch, a cover for closing the housing, the diaphragm assembly being supported on a resilient cantilever arm of a bracket member, calibration means bearing upon the cantilever arm for adjusting the position of the diaphragm, the bracket member being connected to the housing cover by a slip joint, the bracket having a rigid leg extending down from the slip joint and braced against one wall of the housing to lock the slip joint in place, the said resilient cantilever arm of the bracket being hinged to the bottom portion of the rigid leg, the diaphragm assembly being in point contact with the spring mechanism, calibration means bearing upon the spring mechanism for adjusting the tension of the spring mechanism relative to the diaphragm assembly, the spring mechanism having a hinge axis substantially coinciding with the hinge axis of the cantilever arm so there is substantially no relative motion at the point contact during the calibration of the said switch, the electrical switch including an insulating carrier member joined at one end to the spring mechanism as supported in the housing for generally straight motion, said carrier member having a crosshead at its other end with a movable switch contact member supported on each end, a fixed contact means mounted in the housing for engagement by one of the movable contact members respectively, the top fixed contact means is positioned in an inward and upward inclined angle overlying the crosshead to facilitate the 

1. A fixed point, double throw thermal switch comprising an insulating housing with a removable cover, said housing having a separate expansion chamber enclosing both a diaphragm assembly and a snap-acting spring mechanism that is acted upon thereby, said housing also having a pair of electrically isolated switch compartments supporting a double throw switch mechanism, there being an insulating carrier member joining the said spring mechanism to the said switch mechanism, one switch compartment enclosing one set of normally closed switch contacts of the switch mechanism for low temperature operation and the other switch compartment enclosing an alternate set of normally open switch contacts of the switch mechanism for high temperature operation, there being a critical operating temperature for the switch that falls between about 500* F. and about 750* F., whereby at temperatures below the critical temperature, the double throw switch mechanism is in its normal cooking position and at temperatures above the critical temperature, the switch mechanism is in its normal oven cleaning position so that the thermal switch serves as an over-temperature protective means during normal cooking operations and as a lock-out means during a high temperature oven cleaning cycle, said diaphragm assembly being supported on an adjustable bracket member carried by the said housing cover.
 2. A fixed point, thermal switch as recited in claim 1 wherein the adjustable bracket member supporting the said diaphragm assembly is connected adjacent one of its ends to the removable cover, and an adjustable calibration screw extends through the said cover member and engages the opposite end of the bracket for determining the relative position of the diaphragm assembly with respect to the spring mechanism.
 3. A fixed point, thermal switch as recited in claim 1 wherein the adjustable bracket member is connected adjacent one of its ends to the removable cover by a slip joint, said bracket having a rigid leg extending down frOm the slip joint, said leg being braced against one wall of the housing to lock the slip joint in place, said bracket having a resilient cantilever arm rising up and out at an angle from the bottom of the rigid leg, the said diaphragm assembly being mounted on the cantilever arm and having a wear pad seated on a pressure point of the spring mechanism, and a calibration screw means extending through the said cover member and engaging the free end of the cantilever arm for determining the relative position of the diaphragm assembly with respect to the spring mechanism.
 4. A fixed point, thermal switch as recited in claim 3 wherein the adjustable cantilever arm supporting the diaphragm assembly has a hinge axis that substantially coincides with the said hinge axis of the snap-acting spring mechanism such that there is substantially no relative motion between the wear pad of the diaphragm assembly and the pressure point of the spring mechanism during the calibration of the thermal switch.
 5. A fixed point, thermal switch as recited in claim 1 wherein the said double throw electric switch means includes an insulating carrier member joined adjacent one end to the said spring mechanism and being supported for generally straight-line motion, said carrier member having a crosshead with a bridging contact member supported on each end, and two pairs of fixed contacts mounted in the housing, each pair of contacts being adapted to be engaged by one of the bridging contacts, one pair of fixed contacts being mounted in opposition to the other pair such that movement of the carrier in one direction closes the circuit through one pair of fixed contacts and vice versa, and auxiliary spring means acting between the housing and the carrier member to bias the carrier in an angular direction with respect to the direction of movement of the carrier so as to give the carrier a slight rocking action to maintain contact pressure with at least one set of bridging and fixed contacts during the initial creep portion of the spring mechanism before it snaps into its opposite position so as to prevent contact chatter.
 6. A fixed point, thermal switch as recited in claim 5 wherein one pair of fixed contacts is arranged at an acute angle with respect to the direction of movement of the carrier and substantially overhangs the crosshead, and the other pair of fixed contacts is arranged at a transverse angle to the direction of movement of the carrier and underlies the crosshead, the said auxiliary spring means acting in an upward biasing direction to maintain the overhanging set of contacts closed until the spring mechanism snaps into its reversed position.
 7. A hydraulic thermostat comprising a housing enclosing a diaphragm assembly, a snap-acting spring mechanism and an electrical switch means, the diaphragm assembly bearing against the spring mechanism, and the spring mechanism being joined to the switch means for making and breaking an electrical circuit as a function of the expansion and contraction of the diaphragm assembly according to the direction and the extent of the temperature change of a remote body, said housing having a removable cover, said diaphragm assembly being supported from the cover by a bracket member, said bracket having a leg extending down from the cover and a resilient cantilever arm rising up at an acute angle from the bottom of the leg, the diaphragm assembly being mounted to the bottom of the cantilever arm, and a calibration screw means extending through the cover and engaging the free end of the resilient arm for varying the relative position of the diaphragm assembly with respect to the spring mechanism.
 8. A hydraulic thermostat as recited in claim 7 wherein the diaphragm assembly is in point contact with the spring mechanism, the spring mechanism having a hinge axis substantially coinciding with the hinge axis of the cantilever arm so there is substantially no relative motion at the point of contact during the calibration of the said switch means.
 9. A hydraulic thermostat as recited in claim 7 wherein the said bracket member is joined to the cover by a modified bayonet slot connection, said leg of the bracket being braced against one wall of the housing to lock the bracket to the cover.
 10. A hydraulic thermostat as recited in claim 9 wherein the said electrical switch means comprises an insulating carrier member having a crosshead supporting bridging contact means adjacent each end thereof, fixed contact means mounted in the housing for cooperation with the adjacent bridging contact means, and an auxiliary spring means arranged between the housing and the carrier member to bias the carrier into a slight rocking action as it moves upon movement of the diaphragm assembly to maintain contact pressure during the creep portion of the spring mechanism before the spring mechanism snaps so as to avoid contact chatter.
 11. A hydraulic thermostat as recited in claim 9 wherein the said electrical switch means comprises an insulating carrier member having a crosshead supporting a bridging contact means adjacent each end thereof, fixed contact means mounted in the housing for cooperation with the adjacent bridging contact means, one fixed contact means being located beneath the adjacent bridging contact means, the other fixed contact means being disposed at an inclined angle above the other bridging contact means, and an auxiliary spring means acting between the housing and the crosshead to maintain contact pressure between the movable contact and the inclined fixed contact means during the creep portion of the spring mechanism before it snaps and opens this set of contacts and closes the opposite set of contacts.
 12. A hydraulic thermostat comprising a housing enclosing a diaphragm assembly bearing upon a snap-acting spring mechanism that controls an electrical switch, a cover for closing the housing, the diaphragm assembly being supported on a resilient cantilever arm of a bracket member, calibration means bearing upon the cantilever arm for adjusting the position of the diaphragm, the diaphragm assembly being in point contact with the spring mechanism, the spring mechanism having a hinge axis substantially coinciding with the hinge axis of the cantilever arm so there is substantially no relative motion at the point contact during the calibration of the said switch, the said electrical switch including an insulating carrier member joined at one end to the spring mechanism and supported in the housing for generally straight-line motion, said carrier member having a crosshead at its other end with a movable switch contact member supported on each end, a fixed contact means mounted in the housing for engagement by one of the movable contact members respectively, each fixed contact member being mounted in opposition to the other fixed contact member to establish a double throw switch mechanism, an auxiliary spring means acting between the housing and the carrier member to effect holding of one of the set of contacts closed during initial movement of the spring mechanism and until the snap action takes place to reverse the switch setting so as to avoid contact chatter.
 13. A hydraulic thermostat as recited in claim 12 wherein the top fixed contact is positioned in an inward and upward inclined angle overlying the crosshead to facilitate the assembly of the carrier member into the housing, while the lower fixed contact means underlies the crosshead, the said auxiliary spring biasing the carrier in a direction generally toward the top fixed contact means.
 14. A hydraulic thermostat as recited in claim 12 wherein the bracket member is connected to the housing cover by a slip joint, the bracket having a rigid leg extending down from the slip joint and braced against one wall of the housing to lock the slip joint in place, the resilient cantilever arm of the bracket being hinged to the bottom portion of the rigid leg.
 15. A hydraulic thermostat comprising a housing enclosing a diaphragm assembly bearing upon a snap-acting spring mechanism That controls an electrical switch, a cover for closing the housing, the diaphragm assembly being supported on a resilient cantilever arm of a bracket member, calibration means bearing upon the cantilever arm for adjusting the position of the diaphragm, the bracket member being connected to the housing cover by a slip joint, the bracket having a rigid leg extending down from the slip joint and braced against one wall of the housing to lock the slip joint in place, the said resilient cantilever arm of the bracket being hinged to the bottom portion of the rigid leg, the diaphragm assembly being in point contact with the spring mechanism, calibration means bearing upon the spring mechanism for adjusting the tension of the spring mechanism relative to the diaphragm assembly, the spring mechanism having a hinge axis substantially coinciding with the hinge axis of the cantilever arm so there is substantially no relative motion at the point contact during the calibration of the said switch, the electrical switch including an insulating carrier member joined at one end to the spring mechanism as supported in the housing for generally straight motion, said carrier member having a crosshead at its other end with a movable switch contact member supported on each end, a fixed contact means mounted in the housing for engagement by one of the movable contact members respectively, the top fixed contact means is positioned in an inward and upward inclined angle overlying the crosshead to facilitate the assembly of the carrier member into the housing, while the lower fixed contact means underlies the crosshead so as to establish a double throw switch mechanism, and auxiliary spring means acting between the housing and the carrier member in a direction generally toward the top fixed contact means to effect holding the top set of contacts closed during the initial movement of the spring mechanism until the snap action takes place to reverse the switch setting so as to avoid contact chatter. 